The invention relates generally to vacuum sewer systems and, more particularly, to vacuum sewer systems having ejectors for vacuum generation.
In vacuum sewer systems it is known to use ejector devices for generating vacuum. Such systems are disclosed, for example, in patent publications FI 63985 and EP 653524/U.S. Pat. No. 5,535,770. In these vacuum sewer systems the ejector device simultaneously provides a collecting container for the sewage coming from the sewer network. The sewage flow that is circulated by a pump from the collecting container is used as the working medium of the ejector of the ejector device. The suction side of the ejector is connected to the sewer network so that it generates partial vacuum in the sewer network, whereby the sewage coming from the sewer network flows through the ejector into the collecting container. In practice this means that the ejector discharges its working medium, that is the sewage flow circulated by the pump, together with air sucked from the sewer network and the sewage flow coming from the sewer network to the collecting container under high pressure.
Operation of the ejector causes foaming in the collecting container due to the strong jet effect, wherein the foam may be initially transferred to the surroundings through the overflow pipe of the collecting container, through the ventilation duct, and through possible leaks, and may also be transferred into the circulation process of the ejector, lessening the degree of efficiency of vacuum generation. The foaming causes problems with the sewage volume in the collecting container and with the monitoring of the sewage level in the container, which may damage the pump and lead to disturbances in the control functions of the vacuum sewer system. The behavior of the foaming sewage is subject to random changes and it may cause cavitation in the pump. The aforementioned circumstances also reduce the working life of the components of the device. Furthermore, the opening of the device, for example in connection with maintenance or repair, causes a discharge of dangerous gases.
The object of the present invention is to avoid the above mentioned disadvantages and to achieve an arrangement that has a simple structure and a reliable function. Accordingly, a vacuum sewer system is provided for transporting sewage. The system comprises a sewer network including a sewage source and sewer piping adapted to receive sewage from the sewage source. A liquid driven ejector device creates a partial vacuum pressure and includes a primary circuit for circulating liquid functioning as a working medium through the ejector device. The sewer network defines a secondary circuit for transporting waste, and the primary circuit and said secondary circuit are separated from each other.
In accordance with additional aspects of the present invention, an ejector device is provided for generating vacuum in a vacuum sewer system having a sewer network with a sewage source and sewer piping adapted to receive sewage from the sewage source, wherein the sewer network defines a sewage path. The ejector device comprises an ejector container, an ejector having a suction side, and means for circulating a liquid functioning as a working medium of the ejector. A suction connection is connected to the suction side of the ejector and adapted for fluid communication with the sewer network. The ejector container, ejector, and circulating means define a circulation circuit for the working medium for the ejector device, and the circulation circuit is separated from the sewage path.